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Weldability of stainless steels
1. NAME : K.JOTHI KARTHICK
DEPT. : WELDING METALLUGY
REG NO : 1763009
2. Weldability of stainless steels
• There are four types such as
•Austenitic stainless steel
•Ferritic stainless steel
•Martensitic stainless steel
3. WELDABILITY OF AUTENITIC STAINLESS STEEL
• It has the following composition
• C 0.03 to 0.25% Mn 2 to 10%
• Si 1 to 2% Cr 16 to26%
• Ni 3.5 to 22% P and S 0.008% Cb and Ta
• Mo and Ti in somecase fe balance
• They posses high corrosion resistance of all the Stainless
steels.
• They posses great strength and ductility and non magnetic
and so on.
• Application
• Aircraft industry
• Austenitic – process plants, cryogenics, medium corrosive
applications, used over wide temperature range
• Chemical processing (heat exchanger)
• Dairy industry( milk cans)
6. Welding procedure
• Thermal conductivity is low about 50%
• Melting point is low
• Thermal expansion is about 50% lower
• Electrical resistance is about 6 times greater
• The first 4 factor combine require for low
welding current
7. Problems associated with austenitic SS
• Ferrite and sigma phase formation
• Carbide precipitation
• Stress corrosion cracks
• Ferrite and sigma phase formation
This problem is corrected by that electrode that deposit
weld metal containing 3 to 5% of ferrite
• Sigma phase can be redissolved by heating
above 900 degree celsius for short time
Austenite stabilisers, Nieq Ferrite stabilisers, Creq
• Carbon, Nickel, Nitrogen, • Chromium, Molybdenum,v
Manganese, Copper ,Tungsten, Niobium, Silicon
8. Carbide precipitation
• Thermal treatment(845 t0 425 with fast
cooling)
• Use of low carbon SS
• Stabilizer
• Columbium
• Niobium
• Titanium
• tantalum
Stress corrosion cracking(SCC)
• Annealing treatment
• Remove chloride and oxygen
9. Weldability of Ferritic stainless steels
• It has following composition
• C 0.08 to 1.5% Si 1%
• Mn 1 to 2% Cr 11 to 27%
• S 0.04% P 0.04%
• Fe balance
• They possess magnetic and good ductility
• It is more corrosion resist than martensitic steels.
• Application
• Lining petroleum industry
• Heating element for furnace
• Screws and fitting
10. Ferritic SS
• Sensitive to grain growth
– loss of toughness, embrittlement
– limited to 250°C service temperature
– can lead to cracking in weld or HAZ of highly
restrained joints and thick section material.
• Hydrogen cracking
• Filler metals:
• – matching, austenitic or nickel alloy
12. • The welding quality of ferritic Stainless steels
is poorest of AISI types
• Welding heat a zone in the base metal above
critical temp 955 and cause rapid grain
growth of ferrite
• Excess grain growth avoid by lower heat
inputs
• Adding Al,V,Zr to suppress the grain growth
during welding
• Intergranular corrosion avoided by annaling
650 to 815 about 10 min to 60mine
13. Preheating
• A preheating 150 or higher to minimize
residual stress
• Thin section not require
• Thick section require for preheating
PWHT(post weld heat treatment)
• Reduce harness and residual stress
14. Weldability of martensitic Stainless
steels
• It has following composition
• C 0.15 to 3% Si 1.8%
• Mn 3.5% Cr 11 to 18%
• Fe balance Ni 1.25%
• They possess hardness and ductility and magnetic
and so on.
• It is best thermal conductivity of SS.
• It uses of martensitic Stainless steels
• Pump and valve
• Surgical instrument
• Rules an tape
16. • Welding Problems
• Hydrogen cracking
• Normally matching consumables.
• High hardness in the HAZ makes this type of stainless steel
very prone to hydrogen cracking .
• The risk of cracking increasing with the carbon content.
• Above C .15 to 3% not suitable for welding.
• Underbead crack
• Take precautions to minimize
• Preheating
• PWHT
17. Sensitization
• Sensitization refers to the precipitation of
carbides at grain boundaries in a stainless
steel or alloy, causing the alloy to be susceptible
to intergranular corrosion.
• This results in susceptibility to intergranular
corrosion.
• austentitic stainless steel may become sensitised
if they are heat treated or used at temperature in
range 500-800c. the heat affected zones of welds
may also be sensitised in some circumstance
19. CAUSES
• More amount of carbon content
• Slow rate of cooling from 425 to 845 so it is
also called sensitising temperature range.
• Time ,temperature , chemical composition
play a vital role in sensitisation.
20. Prevention
• Fast cooling requires because the carbon does
not react with chromium.
• Stabilizer
• Columbium
• Niobium
• Titanium
• Tantalum
• Both base materials and fill rod have low
carbon content.
21. Sigma embrittlement
• Sigma phase is a non-magnetic composed mainly of
iron and chromium which forms in ferritic and
austenitic stainless steels during exposure at 560º-
980ºC .
• Many stainless steels and other iron-chromium alloys
are susceptible grain boundary phenomenon known
as sigma-phase embrittlement.
• Alloy elements such as molybdenum, titanium and
silicon promote the formation of sigma phase
• Molybdenum promotes sigma-phase formation much
more effectively than chromium, particularly at
temperatures around 900°C (1650°C)
23. causes
• Loss of ductility and toughness
• Corrosion resistance resulting in cracking
• Failure of components
• Especially those subjected to impact loads or
excessive stress
25. Mode of solidification
• Solidification
solidification, also known as freezing, is a phase
change of matter that results in the production of a
solid. Generally, this occurs when the temperature of
a liquid is lowered below its freezing point
• There are four modes
• Planar
• Cellular
• Columnar Dendrite
• Equiaxed dendrite
